1. Field of the Invention
The present invention relates to an improved contact assembly for a high-voltage circuit interrupter and, more particularly, to an improved female contact for a high-voltage circuit interrupter protecting an alternating-current circuit, which female contact is simpler to manufacture and lower in cost than prior art female contacts and exhibits longer life and greater resistance to damage caused by sustained high-voltage arcing within the interrupter.
2. Brief Discussion of the Prior Art
High-voltage circuit interrupters, such as circuit switchers and other puffer-type interrupters, are well known in the prior art. These circuit interrupters typically comprise normally engaged main contacts and normally engaged arcing (or interrupting) contacts. When the interrupter is closed, current may pass between the engaged main contacts. When a fault current or other overcurrent in a circuit protected by the interrupter is sensed by appropriate detectors, the main contacts are opened in response thereto. In order to "protect" the main contacts, that is, in order to prevent arcing therebetween, a current path is established between the arcing contacts before the main contacts separate. Thus, no arcing occurs between the main contacts. Following separation of the main contacts, the arcing contacts separate and arcing is initiated therebetween. As the interrupter is closed, the arcing contacts engage before the main contacts engage. The arcing contacts are typically made of a refractory metal in order to withstand the numerous arcing events which may occur during opening and closing of the circuit interrupter. Since the arcing contacts are not relied upon to provide the normal current path through the interrupter, any "damage" that they do sustain as a result of arcing events does not effect the ability of the interrupter to carry current, which ability results from the "protection" of the main contacts, as described.
Whether comprising main contacts or arcing contacts, a typical prior art contact structure comprises a female contact and a male contact. When the main contacts are closed, they engage, with the male contact being telescoped into the female contact. When the contacts separate to open, the male contact moves out of the female contact and away therefrom. Often, the main contacts and the arcing contacts of high-voltage circuit interrupters each comprise a male-female contact pair, with each pair being mechanically related to the other pair so that there is some "overlap" between the opening and closing thereof. This "overlap" permits the main contacts to separate prior to separation of the arcing contacts during opening of the interrupter and permits the arcing contacts to engage prior to engagement of the main contacts during closing of the interrupter.
The cost of high-voltage circuit interrupters is lowered if, instead of using two male-female contact pairs, a single male-female contact pair functions as both the main contacts and the arcing contacts. Obviously, the elimination of one contact pair also simplifies the circuit interrupter. To these ends, the male contact has included an elongated, conductive rod carrying a refractory tip at the free end thereof, and the female contact has included a cylindrical array of flexible, conductive, spaced fingers which define a cavity into and out of which the male contact may be telescoped. The fingers are biased inwardly toward the axis of the cavity. Free ends of the fingers carry refractory tips which define therebetween an aperture continuous with the cavity. When the contacts are closed and the male contact is within the cavity, current passes between the engaged rod and fingers acting, therefore, as the main contacts. As the contacts open, the rod "leads" the tip thereon in exiting the cavity and the aperture. At some point during this exiting after the main contacts--the rod and the finger--separate, the tip on the rod and the tips on the fingers engage, the engaged tips, therefore, momentarily carrying the current in the interrupter and act as the arcing contacts. Finally, the arcing contacts--the refractory tips--separate and high-voltage arcing is initiated therebetween. As the contacts close, engagement of the tips "leads" engagement of the rod and the fingers so that any arcing occurs between the tips.
In typical prior art female contacts of the type described above, the refractory tips are brazed or welded to the free ends of the fingers. The female contact has been fabricated by brazing or welding a refractory metal ring to one end of a metal tube and thereafter forming a series of parallel, elongated cuts or slits in the ring and the tube to define the plurality of fingers with the refractory tips on the free ends of each thereof. The female contact has also been fabricated by first forming the fingers in any convenient manner and then welding or brazing individual tips to the free ends thereof.
Several deficiencies have been noted in the above-described female contacts of the prior art. First, the brazing or welding of the refractory ring or tips to the conductive tube or the fingers increases manufacturing costs. Second, during operation of an interrupter containing the prior art female contact, sustained arcing to one finger or its tip may degrade or destroy the brazing or weldment between the tip and its finger, causing the tip to become dislocated. Dislocation of the tip may jam the circuit interrupter by interferring with the free relative movement (during opening or closing) of the contacts. Third, sustained arcing to one finger or its tip is encouraged when the female contact is constructed, as described above, that is, where the fingers and their tips are spaced apart or are formed by the parallel cuts or slits. Specifically, the spacing of the fingers and their tips (whether produced by the cuts or slits, or otherwise) provides sharp edges or corners on which a high-voltage arc may "root" or preferentially terminate. Such rooting of an arc may result in undue heating of the finger and its tip leading to the possible result that the brazing or weldment therebetween will be degraded or destroyed and that dislocation of the tip occurs.
As a consequence of the above, a primary object of the present invention is the provision of improved contact structure for a high-voltage circuit interrupter in which the main contacts and the arcing contacts constitute a single male-female contact pair, and in which the structure of the female contact is improved to obviate or eliminate the above-described problems and difficulties inhering in prior art female contacts.